Benzoyl peroxide (BPO) is one of the important oxidant compounds used as a free radical initiator in plastic production, as a bleaching agent in food and as a drug compound of acne treatment in cosmetic and pharmaceuticals industries. It is a progression agent in mouse skin carcinogenesis because it has tumor promoter activity and also strong cytotoxic activity. In this study, we have investigated the clastogenic effects of BPO with CBMN assay in human blood lymphocyte cultures. BPO at final concentrations of 10(-5) M, 10(-6) M, and 10(-7) M was tested in peripheral bloods obtained from eight healthy male and eight female donors. According to data, the frequency of cells with micronuclei showed a statistically significant dose increase in a dependent manner compared with negative controls. Comparing the two donor groups, the differences in the mean counts were not significant. Increasing micronucleus rates showed that BPO could have clastogenic effect in human lymphocytes.